256 THE REPTILES 



do not belong to the snakes at all, but are lizards in which external 

 limbs have either totally disappeared, or are only present in a 

 rudimentary condition ; in most the internal shoulder and pelvic 

 girdles characteristic of the lizards can be traced. 



The existing snakes may be conveniently grouped under three 

 headings, two of which contain the poisonous species : (i) the 

 Viperiform Snakes ; (2) the Venomous Colubrines ; and (3) the 

 True Colubrines or Innocuous Snakes. Many snakes live a forest 

 life, climbing the trees and moving from branch to branch ; others 

 live on the ground, rarely, if ever, taking to trees ; a few lead 

 a burrowing life, and some are water snakes, frequenting fresh 

 water and the sea; All the marine forms are poisonous, belonging 

 to the Venomous Colubrines. 



With very few exceptions the snakes are covered with scales, 

 which are true skin structures and are periodically shed. The 

 presence of plates on the head, the arrangement and character of 

 the scales on the. upper and under surface of the body and tail, 

 and their colour and ornamentation, are all points useful in the 

 classification of these reptiles; We have seen that some of the 

 amphibia and lizards are very snake-like in appearance, being 

 destitute of external limbs, and some of the lizards have one of 

 the lungs ill-developed, the other preponderating, as is the case in 

 all snakes ; while the Boas and Pythons have minute vestiges 

 of hind limbs, scale-like or spine-like, close to the vent. But an 

 examination of the internal organs, and especially of the bony 

 framework of the snake's body, soon demonstrates the distinct- 

 ness of the snakes from the lizards. The snakes and limbless 

 lizards appear as examples of degenerate evolution, and as the 

 descendants of reptiles which did not crawl on their belly 

 but had in perfection those organs of locomotion that are 

 rudimentary or absent in their descendants. 



The venom of a snake is secreted by a gland on each side of 

 the front part of the skull, which is close to the maxillary bones 

 that support the long and more or less curved poison fangs. 

 The duct of each gland leads either to a groove in the front part 

 of the fang or to a canal in the tooth formed by the union of the 

 sides of a groove, and in both instances the liquid poison enters 

 the victim with the tooth, and some is left behind. Those snakes 

 which have the first fangs of the upper jaw grooved along their 



